The semiconductor integrated circuit industry has experienced rapid growth in the past several decades. Technological advances in semiconductor materials and design have produced increasingly smaller and more complex circuits. These material and design advances have been made possible as the technologies related to processing and manufacturing have also undergone technical advances. In the course of semiconductor evolution, the number of interconnected devices per unit of area has increased as the size of the smallest component that can be reliably created has decreased.
One broad category of commonly used techniques employed to form material layers and alter properties over semiconductor wafers is deposition, which includes the techniques such as chemical vapor deposition, physical vapor deposition, sputtering, ion implantation, etc. In many some kinds of deposition, plasma is used to produce chemically reactive species above wafer surface undergoing the deposition process. As technology scales, the need for atomic thickness control and high conformity and quality of deposited layers is desired. Atomic Layer Deposition (ALD) is a thin film deposition technique that is based on the sequential use of a gas phase chemical process and is one deposition process that may be enhanced by the use of plasma. ALD deposition typically use gases chemicals, typically called precursors, which react with the surface of a target substrate one at a time in a sequential, self-limiting, manner. Through the repeated exposure to separate precursors, a thin film is slowly deposited.
“Plasma enhanced” ALD (PE-ALD) processes use plasma which is a mixture of ions, electrons, neutral excited molecules. PE-ALD maintains use of specific chemical precursors as in ALD as described above. However, the plasma is used to create the necessary chemical reactions in a highly controlled manner. Further, PE-ALD allows for radical species to be used in the deposition at lower process temperatures and often developing better film properties than in thermal ALD processes.
These figures will be better understood by reference to the following detailed description.